Different from crystalline polyesters such as polyethylene terephthalate and polybutylene terephthalate, liquid crystal polyesters do not entangle in their molecules even in the molten state due to their rigidity to form polydomains in the liquid crystal state, and show the behavior that the molecular chains are significantly orientated in a flow direction by low shear. They are generally referred to as melt type liquid crystal (thermotropic liquid crystal) polymers. The liquid crystal polyesters have very excellent melt flowability due to this characteristic behavior, and thin-walled molded articles having a thickness of about 0.2 to 0.5 mm can be easily obtained. Moreover, the molded articles offer the advantages of high strength and high stiffness. However, they also have the disadvantages of very large anisotropy and significantly low weld strength. Furthermore, high molding temperatures thereof have limited their use. The liquid crystal polyesters also have the problem that they are generally expensive.
Inexpensive liquid crystal polyester resin compositions retaining the excellent thermal resistance and mechanical properties of the crystal polyesters and having improved in weld strength of their molded articles have been strongly demanded from the market.
A resin composition comprising a melt-processable polymer and an anisotropic melt forming polymer is disclosed in JP-A-56-115357 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), wherein it is described that addition of the anisotropic melt forming polymer to the melt-processable polymer results in an improvement in processability of the melt-processable polymer. For example, addition of a liquid crystal polyester to a polyphenylene ether/polystyrene mixture is exemplified therein.
For the purpose of improving solder heat resistance, resin compositions in which liquid crystal polyesters are blended with various kinds of polyarylene oxides are described in JP-A-2-97555.
However, in general, a composition formed by blending a liquid crystal polyester having a higher molding temperature with an amorphous polymer such as polyphenylene ether having a lower molding temperature than that of the liquid crystal polyester has the disadvantage of producing a molded article with poor appearance due to thermal decomposition of the blended resin on molding processing at high temperatures, although the melt processability of the composition is improved. Further, the composition has the problem that it insufficient in thermal resistance, mechanical properties, and impact resistance.
Compositions comprising liquid crystal polyesters and aromatic polycarbonates are disclosed in JP-A-57-40551, JP-A-2-102257, etc. However, they are not sufficient in thermal resistance and mechanical properties.
The present invention provides inexpensive liquid crystal polyester resin compositions retaining the excellent thermal resistance, mechanical properties and thin wall properties inherent in the liquid crystal polyesters, and improved in molding processability and in weld strength and impact resistance of their molded articles.